Yes I see. That wiring is a bit different from the 80 or the 4Runner wiring. I still don't think you will have any trouble with one 20A circuit.
There is a 10A (guess?) fuse on the other side of the instrument cluster which isn't shown on this diagram. That's the 10A that I was referring to.
Btw, here are a couple of places to buy the trailor cord:
http://www.wiringproducts.com/index1.html
http://www.rjays.com/Rjays_electrica...er-cords-1.htm